#### Answer

$=\cos 45=\dfrac {\sqrt {2}}{2}$

#### Work Step by Step

$1-2\sin ^{2}\alpha =\cos 2\alpha \Rightarrow 1-2\sin ^{2}22\dfrac {1}{2}=\cos \left( 2\times \left( 22\dfrac {1}{2}\right) \right) =\cos 45=\dfrac {\sqrt {2}}{2}$

Published by
Pearson

ISBN 10:
013421742X

ISBN 13:
978-0-13421-742-0

$=\cos 45=\dfrac {\sqrt {2}}{2}$

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